Comprehensive Anatomy and Clinical Considerations of the Nose and Paranasal Sinuses ch 27

External and Internal Anatomy of the Nose

• The nose and the nasal cavity consist of a complex arrangement of hard and soft tissues. The external nose is the portion of the nasal complex that protrudes outward from the skeletal component.

• The external nose is attached superiorly to the nasal bones and inferiorly to the anterior nasal spine.

• Each protruding lateral margin is known individually as a wing of the nose, or an ala.

• The external nose is divided in half by the cartilaginous part of the nasal septum, which is the wall dividing the nasal complex into right and left halves ($27.1$).

• The nasal aperture, which is the anterior-most portion of the nasal cavity visible on a skull, is somewhat pear-shaped.

• The nasal septum inside the cavity is formed from the following structures:

  • The vomer bone.

  • A portion of the ethmoid bone.

  • The fibrocartilaginous part of the septum ($27.2$).

• The lateral walls of the nasal cavity feature $3$ shelves known as nasal conchae, which project into the septum.

• The superior portion of the bony nasal cavity contains small holes that open into the anterior cranial fossa through the cribriform plate of the ethmoid bone. These holes transmit olfactory nerves from the nose to the brain.

• The inferior portion or floor of the nasal cavity is formed by the bones of the hard palate, which include:

  • The palatal processes of the maxillae.

  • The horizontal portion of the palatine bones.

• The upper $\frac{1}{2}$ to $\frac{2}{3}$ of the lateral wall of the nasal cavity is formed from parts of the ethmoid bone.

Clinical Considerations: Pituitary Gland Access

• Advances in fiberoptics and microscopic instruments allow surgery on pituitary gland tumors to be performed through the nasal cavity rather than through the skull.

• The procedure involves entering the nasal cavity, moving into the sphenoid sinus, and cutting away the roof of that sinus to gain access to the pituitary gland from below.

• The pituitary fossa is used as a cephalometric landmark in orthodontics.

• The deepest part of the pituitary fossa is called the sella turcica ($27.3$).

• The pituitary gland is housed within the pituitary fossa.

Epithelial Tissues and Respiratory Mechanism

• The nasal cavity is the beginning of the respiratory tract or system.

• The primary lining of the respiratory tract is respiratory epithelium, which is a pseudostratified columnar epithelium with goblet cells.

• The epithelium features many hair-like projections called cilia. These move in a synchronized beating pattern toward the anterior portion of the nasal cavity.

• Goblet cells secrete a sticky mucous substance onto the cilia. This mucus traps contaminants entering the nasal cavity.

• Foreign material is moved toward the front of the nose, where it is removed by blowing the nose. During sleep, this mucus may flow backward, a process known as postnasal drip.

• The nasal conchae function to increase the surface area within the nasal cavity to maximize the efficiency of this filtering mechanism.

• Olfactory epithelium is a modified epithelium containing nerve fibers that perceive odors. It is located in the roof of the nasal cavity and extends onto the upper surface of the superior concha and the upper nasal septum.

Paranasal Sinuses: Overview and Location

• The paranasal sinuses are compartments or cavities of various sizes that open into the nasal cavity.

• There are $4$ pairs of paranasal sinuses:

  • $2$ ethmoids.

  • $2$ frontals.

  • $2$ maxillaries.

  • $2$ sphenoids.

• The nasal conchae must be located to see these openings; they provide shelter for areas known as meatuses.

• Inferior meatus: Located beneath the inferior nasal concha. It contains the opening of the nasolacrimal duct, which carries tears from the corner of the eye into the nasal cavity.

• Middle meatus: Lies beneath the middle nasal concha. It contains the hiatus semilunaris, which is a crescent-shaped or half-moon-shaped opening. The ethmoid bulla is the bulbous ridge located above the hiatus semilunaris.

• Superior meatus: Lies beneath the superior concha and is the smallest of the meatuses ($27.4$).

• Sphenoethmoidal recess: The highest and most posterior part of the nasal cavity where the sphenoid sinuses open.

Detailed Anatomy of Sinus Groups

• Frontal Sinuses:

  • Located in the frontal bone just above the orbital cavity.

  • Size varies per individual; they frequently cross the midline and may be partially located on the opposite side.

  • They drain into the very anterior end of the hiatus semilunaris.

  • Infection causes pressure and pain directly above the eye.

• Sphenoid Sinuses:

  • Located in the body of the sphenoid bone, just underneath the pituitary fossa in the middle cranial fossa.

  • These sinuses also cross the midline and open into the sphenoethmoidal recess.

  • Infection causes deep pressure and a congested feeling in the midline of the head that is difficult to localize.

• Ethmoid Sinuses:

  • Often called ethmoid air cells because they are subdivided into numerous small compartments rather than being single-paired sinuses.

  • Subdivided into anterior, middle, and posterior clusters.

  • Anterior ethmoid air cells: Located at the base of the middle nasal concha. They open into the hiatus semilunaris posteroinferior to the frontal sinus opening.

  • Middle ethmoid air cells: Located in the base of the middle nasal concha, behind the anterior cells, and within the ethmoid bulla. Openings may be found on the ethmoid bulla or in the hiatus semilunaris.

  • Posterior ethmoid air cells: Located in the base of the superior nasal concha and open into the superior meatus.

  • Infections are particularly difficult to treat due to the small, subdivided compartments and cause congestion and aching within the nasal cavity area.

Clinical Observations and Pathophysiology of the Maxillary Sinus

• The maxillary sinuses are the largest paranasal sinuses. They open into the posterior end of the hiatus semilunaris via one or more openings.

• Development and Size:

  • At birth: Approximately the size of a small pea in each maxilla.

  • Young Adult: Extends anteroposteriorly from just posterior to the maxillary canine to the third molar area.

  • Superoinferiorly: Extends from the floor of the orbital cavity to the root tips of the maxillary posterior teeth ($27.5$).

• Drainage Challenges:

  • The opening for the maxillary sinus is located almost $\frac{2}{3}$ of the way up the medial wall of the sinus.

  • Draining a cavity from an opening near the top is difficult.

  • Nasal infections cause mucosal edema (swelling). If the sinus opening is small, it may swell shut.

  • A closed, warm sinus acts as an incubator for microorganisms, increasing the severity of infection.

  • Fluid buildup causes pressure to increase when the head is tilted forward, as fluid flows against the anterior wall.

  • Temporary relief may be found via nasal sprays or tilting the head to one side while lying down to allow drainage from the "high-side" sinus.

• Chronic clogging may require an ENT specialist to punch and enlarge a hole from the inferior meatus into the medial wall of the maxillary sinus near its base to facilitate drainage.

Dental Considerations and Surgical Complications

• Nerve Supply and Referred Pain:

  • Sensory nerves that supply maxillary posterior teeth also supply the maxillary sinuses.

  • The brain is accustomed to receiving constant sensory messages (e.g., from biting) from the teeth via these nerves.

  • During a sinus infection, messages sent from the sinus are often misinterpreted by the brain as coming from the teeth, resulting in a "false toothache."

  • Diagnostic indicators of sinus-related pain rather than dental caries include: absence of caries or periodontal pockets, only mild sensitivity to percussion, normal pulp test results, and cloudiness in the maxillary sinus on a periapical radiograph (signifying fluid buildup).

  • Patient history of recent sinus problems is a critical diagnostic step.

• Relationship to Tooth Roots:

  • The floor of the maxillary sinus may dip down around the root tips of posterior teeth.

  • Periapical infections of a tooth can potentially involve the sinus.

  • The sinus may dip between the roots of a maxillary molar.

• Extraction Hazards:

  • Dilacerated roots (roots curved due to developmental disturbances) present a risk of extracting part of the maxillary sinus floor during tooth removal.

  • Reliable radiographs are required to assess the relationship between roots and the sinus floor; failure to do so may be considered negligent treatment.

  • To minimize fracture risk in teeth with dilacerated roots, roots should be sectioned and removed individually.

  • Following the extraction of maxillary teeth and healing, the maxillary sinus often enlarges into the space formerly occupied by roots or impacted third molars, thinning the bone of the maxillary tuberosity and alveolar ridge.

• Functions of Sinuses:

  • Historical theory: Sinuses warm the air passing into the respiratory system (now considered minimal due to low airflow).

  • Current theory: Sinuses function to lighten the overall weight of the skull bones.

Questions & Discussion

• How should a dental professional proceed if a patient complains of a severe toothache but shows no clinical signs of caries or periodontal disease?

• First, perform clinical tests including percussion and pulp testing and review periapical radiographs for lesions or sinus cloudiness. If results are normal, check the medical and dental history for sinus infections. If the patient confirms sinus issues, refer them to a physician for treatment.

• What is the significance of sinus expansion after tooth extraction?

• The maxillary sinus tends to enlarge into the area once occupied by the posterior maxillary roots. This results in thin bone in the maxillary tuberosity and alveolar ridge, which must be evaluated when planning prosthetic appliances to replace missing teeth.